Scroll compressors are well known as compressors for compressing the gas used in the cooling systems of refrigerators, freezers and air conditioners, etc. These scroll compressors have a scroll compressing unit with a pair of scroll members having interfitting spiroidal wraps. These scroll compressors are compact, highly efficient, and have low vibration, making them suitable for a wide range of applications.
This kind of scroll compressor has a sealed housing on the inside of which a frame, which divides the housing into upper and lower sections, is fastened. The scroll compressing unit is arranged on the upper part of this frame, and the motor for driving the scroll compressing arrangement is located on the lower part of the frame. Lubricating oil is collected at the bottom of the sealed housing.
In general, the scroll compressing unit consists of a stationary scroll member and an orbiting scroll member. The stationary scroll member and the orbiting scroll member have an end plate and a wrap projecting at right angles to the end plate. A shaft bearing passes through the frame and supports the rotary shaft of the motor.
A rotation transmission mechanism and an Oldham mechanism are provided between the upper part of the drive shaft and the orbiting scroll member to orbit the orbiting scroll member around the axis of rotation of the drive shaft.
As the space inside the motor equipped housing serves to separate the air and the liquid, the lower part of the orbiting scroll member is given a low pressure atmosphere, and the suction pipe is connected to this low pressure atmosphere. The upper part of the stationary scroll member is given a high pressure atmosphere, and the discharge pipe is connected to this high pressure atmosphere. Accordingly, a compression chamber is formed between the wraps of both the stationary scroll member and the orbiting scroll member, thereby forming a passage from the suction pipe to the discharge pipe via the compression chamber.
With this kind of construction, however, gas pressure inside the compression chamber increases as the orbiting scroll member orbits. Accordingly, the orbiting scroll member receives a downward thrust. In a 5-hp machine, this downward thrust may be as high as several hundred kilograms, resulting in an increase in the friction loss in the sliding part of the Oldham mechanism, for example. Because of this, the input must be increased, which increases the possibility of seizure. Also, when the downward thrust is large, the wraps of both the stationary scroll member and the orbiting scroll member are pressed in the axial direction to separate both scroll members from each other, resulting in a gap between the end plate of one of both scroll members and the wrap of the other, which in turn results in leakage of the pressurized gas.
In order to solve these two drawbacks, Eiji Sato in the U.S. application, Ser. No. 887,252, Mar. 16, 1978 proposed providing an intermediary chamber sealed off by the back surface of the orbiting scroll member. Part of the compressed gas from an intermediary compression chamber is fed into this intermediary chamber, and the orbiting scroll member is pressed against the stationary scroll member by the pressure of the gas in the intermediary chamber.
With this proposed device, however, the intermediary chamber is formed around the drive shaft of the motor, so a difference arises between the pressure in the housing and the pressure around the drive shaft. Consequently, when a centrifugal pump is employed at the motor drive in supplying lubricating oil to the individual friction parts, this pressure difference will result in over supply of oil to these parts, and in insufficient oil at the bottom of the housing. Also, it is necessary to use ball bearings and impregnated metal for the bearings in the friction parts around the drive shaft in the intermediary chamber. The reason for this is that, when the motor is started, there is no pressure difference between the housing and the intermediary chamber, and the result is insufficient lubrication between the bearing in the frame and the drive shaft. Accordingly, the construction for this type of compressor is complicated and the cost is high.
Tojo et al in U.S. Pat. No. 4,365,941, Apr. 30, 1980, proposes an intermediary chamber type compressor in which the bearing construction is simple. With this device, however, the previously mentioned drawback is not overcome. Moreover, because the discharge pipe is connected to the lower portion of the housing, which contains the motor, it is impossible to use the lower portion of the housing to separate the air and liquid.